Micro-fabricated alkali vapor cells sealed at low temperatures with thin-film metallic bonding

We report on the characterization of micro-fabricated alkali vapor cells, sealed by low-temperature thin-film metallic bonding. The low sealing temperatures ≤ 140°C are of high interest in view of future micro-fabricated cells using anti-relaxation wall coatings. Long-term measurements using saturated-absorption and double-resonance spectroscopy show a stable pressure inside the cells and therefore an excellent hermeticity of the bonding over several months. This is also confirmed by independent leak-rate measurements of indium bonded sample cells by a membrane deflection method.